The present invention relates to a plastics injection-molding machine with an electrical rotary drive and electrical linear drive.
As a drive, in particular as an injection and metering system, in a plastics injection-molding machine or in similar machine applications, it is necessary to provide a rotary movement and a linear movement on the drive shaft. It must be possible to produce these movements on the one hand independently of one another, or else superimposed.
Until now, a movement such as this with two degrees of freedom has been achieved by the use of two separate, rotary drives. FIG. 1 shows a cross section through one such drive. A threaded spindle 1 is driven via a first spindle nut 2 by a first rotary drive 3 and via a second spindle nut 4 by a second rotary drive 5. The threaded spindle 1 is used to convert the rotary movement to a linear movement. The functional principle can be explained with the aid of FIG. 2, which schematically illustrates the output drive shaft or threaded spindle 1 and the spindle nuts 2, 4. When the spindle nuts 2, 4 are driven in the same direction and at the same rotation speed, this results in a purely rotary movement. If, in contrast, the two rotary drives are driven at the same rotation speed in opposite directions then this leads to a pure linear movement of the threaded spindles. If the rotary drives are operated at different rotation speeds and/or in different rotation directions, this results in a combined rotary-linear movement. This drive has the disadvantage on the one hand of the relatively complicated control system, since the threaded drive mechanism must also be taken into account in the operation of the two rotary motors in order to achieve a linear movement. Furthermore, two motors must always be controlled in synchronism for simple movements. The control loop for the linear drive is also relatively complex. A further major disadvantage is that the threaded drive mechanism as well as the bearings are subject to a relatively large amount of wear. This is because these components have to absorb large axial forces. A further disadvantage is that the entire drive is physically relatively large.